Pyrolysis is a general term used to describe the thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. Pyrolysis differs from other high-temperature processes like combustion and hydrolysis in that it usually does not involve oxidative reactions and is often characterized by irreversible simultaneous change of chemical composition and physical phase.
Pyrolysis is a case of thermolysis, and is most commonly used for organic materials, and is one of the processes involved in charring. Charring is a chemical process of incomplete combustion of certain solids when subjected to high heat. The resulting residue matter is called char. By the action of heat, charring reductively removes hydrogen and oxygen from the solid, so that the remaining char is composed primarily of carbon in a zero oxidation state. Polymers such as thermoplastics and thermoset, as well as most solid organic compounds like wood and biological tissue, exhibit charring behavior when subjected to a pyrolysis process, which starts at 200-300° C. (390-570° F.) and goes above 1000° C. or 1800° F., and occurs for example, in fires where solid fuels are burning. In general, pyrolysis of organic substances produces gas and liquid products and leaves a solid residue richer in carbon content, commonly called char. Extreme pyrolysis, which leaves mostly carbon as the residue, is called carbonization.
The pyrolysis process is used heavily in the chemical industry, for example, to produce charcoal, activated carbon, methanol, and other chemicals from wood, to convert ethylene dichloride into vinyl chloride to make PVC, to produce coke from coal, to convert biomass into syngas and biochar, to turn waste into safely disposable substances, and for transforming medium-weight hydrocarbons from oil into lighter ones like gasoline. These specialized uses of pyrolysis are called by various names, such as dry distillation, destructive distillation, or cracking. Efficient industrial scale pyrolysis has proven to be difficult to perform and adjust reactor conditions to feedstock variations in order to achieve a desired degree of carbonization.
Cogeneration also referred to as combined heat and power (CHP) is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat. All thermal power plants emit a certain amount of heat during electricity generation. The heat produced during electrical generation can be released into the natural environment through cooling towers, flue gas, or by other means. By contrast, CHP captures some or all of the by-product heat for heating purposes, or for steam production. The produced steam may be used for process heating, such as drying paper, evaporation, heat for chemical reactions or distillation. Steam at ordinary process heating conditions still has a considerable amount of enthalpy that could be also be used for power generation.
Transforming waste from a liability to an asset is a high global priority. Currently employed technologies rely on incineration to dispose of carbonaceous waste with useable quantities of heat being generated while requiring scrubbers and other pollution controls to limit gaseous and particulate pollutants from entering the environment. Incomplete combustion associated with conventional incinerators and the complexities of operation in compliance with regulatory requirements often mean that waste which would otherwise have value through processing is instead sent to a landfill or incinerated off-site at considerable expense. Alternatives to incineration have met with limited success owing to complexity of design and operation outweighing the value of the byproducts from waste streams.
To address this global concern, many methods have been suggested to meet the flexible needs of waste processing. Most of these methods require the use of a waste processing reactor, or heat source, which are designed to operate at relatively high temperature ranges 200-980° C. (400 to 1800° F.) and allow for continuous or batch processing.
An essential element of chemical reactors used in waste processing is for a reactor to enhance mixing and reduce variable reactive conditions associated with spatial variation in the waste material being processed. It should be appreciated that these features should be optimized in order to create conditions which maximize heat diffusion, through material convection, in order to reduce the amount of processing time. While those variables are readily controlled in pilot scale systems, industrial scale processing has proved difficult.
Various reactor feed and waste treatment devices are currently available in the industry. Many devices operate to produce a steady flow of material to a reactor, with varying methods of compaction. These conventional devices are not satisfactory, however, in that they are not versatile enough to process and adequately compress the variety of waste materials.
Currently, many conventional waste treatment devices utilize a compression auger-screw to shred and compact various waste forms for disposal and further processing. However, these devices usually have a fixed compression ratio which cannot account for the various types of waste materials to be processed.
Thus, there exists a need for a waste processing reactor which can transform a waste stream from a liability on an industrial scale and without allowing contaminant release. There further exists a need for a process of waste reaction that is efficient to operate to limit environmental pollution in the course of such a transformation, and to produce useful co-products that aid on the overall economic value of the process.